In the orthopedic implant field, the replacement of entire human skeletal joints is well established as every day surgical procedures calling for the permanent attachment of metallic joint parts to the existing bone structure. A usual method of attachment, particularly in the case of total hip joint replacement, employs metal screws of various diameters and lengths. The placement of such screws requires that a precisely located pilot hole is driven into the bone structure at the correct angle and depth and diameter as specified by the manufacturer of the implant part and subject to the operating surgeon's evaluation of the bone condition as observed in both pre-operation x-rays and upon opening the joint. As many as three screws may be inserted to hold an acetabular cup in place and of the correct diameter and length. This can require the surgeon to rapidly select the correct drill bit, hold it at the correct angle with the help of a drill guide and drill to the correct depth. The latter requirement is aided by the choice of several drill bit lengths and using the correct bit, drill until the drill holder bottoms out on the drill guide.
The surgeon may be forced to make several drill bit changes in a single operation. Existing bits require his visual attention as well as the use of both hands to make a bit change, if he does so himself. Otherwise, he must rely upon other operating room personnel to rapidly exchange bits and install the bits properly, particularly to produce the correct diameter and depth hole.
Some drill bits include flexible shafts as a permanent part of the bit, increasing their cost significantly and require the discarding of not only the bit but the flexible shaft when the normally unresharpened bit becomes dull.
Other types of drill bits have accomplished a degree of modularity in that the bit is separate from the flexible drive and uses a form of collet. Longitudinal positioning and torque transfer to the bit is achieved via a cross bar which is brazed in a transverse hole in the bit shank. This type of bit and collet assembly is a step forward but it requires the removal of a part of the collet assembly with each bit change. It also allows a bit to be placed in the collet without being secured either longitudinally or in torque transfer relationship. This might only be discovered as the surgeon begins drilling erratically--truly an unsatisfactory situation.